Conventional shower doors have glass doors sliding on a rail with the aid of guiding means consisted of pulley wheels and connecting means for connecting the pulley wheels to the glass doors. The pulley wheels are extended into the rail so as to be able to roll along the rail such that the glass doors are slidable. When there are two panels of movable glass door, the movement of the one of the two panels is actuated by collision with the other. The collision between the two doors makes noise and shock which is undesirable. Alternatively, the movements of the two panels are synchronized through a synchronization means. However, the synchronization often fails due to the failure of the connection between the synchronization means and the wheels.